Deep learning is a technology used to cluster or classify objects or data. For example, computers cannot distinguish dogs and cats from photographs alone. But a human can easily distinguish those two. To this end, a method called “machine learning” was devised. It is a technique to allow a computer to classify similar things among lots of data inputted into the computer. When a photo of an animal similar to a dog is inputted, the computer may classify it as a dog.
There have already been many machine learning algorithms to classify data. For example, a decision tree, a Bayesian network, a support vector machine (SVM), an artificial neural network, etc. have been developed. The deep learning is a descendant of the artificial neural network.
Deep Convolution Neural Networks (Deep CNNs) are the heart of the remarkable development in deep learning. CNNs have already been used in the 90's to solve the problem character recognition, but their use has become as widespread as it is now thanks to recent research. These deep CNNs won the 2012 ImageNet image classification tournament, crushing other competitors. Then, the convolution neural network became a very useful tool in the field of the machine learning.
FIG. 1 shows an example of various outputs to be acquired from a photograph using a deep CNN according to prior art.
Classification is a method for identifying a type of a class to be acquired from a photograph, for example, as shown in FIG. 1, determining whether an acquired object is a person, a lamb, or a dog. Detection is a method for finding every object and displaying the found object as enclosed in a bounding box. Segmentation is a method for distinguishing a region of a specific object from other objects in a photograph. As the deep learning has recently become popular, the classification, the detection, and the segmentation are using the deep learning heavily.
FIG. 2 is a diagram schematically illustrating a detection method by using the CNN.
By referring to FIG. 2, the learning device receives an input image and applies a plurality of convolution operations to the input image through a plurality of convolutional filters (or convolutional layers) to thereby generate at least one feature map. Then, the learning device allows the feature map to pass through a detection layer to thereby generate at least one bounding box, and then allows the bounding box to pass through the filtering layer to thereby generate a final detection result. Thereafter, backpropagation is performed by using a loss value obtained by referring to the detection result and its corresponding a ground truth (GT) value which has been annotated by a person in advance to thereby allow a detector (i.e., the CNN learning device) to gradually make the detection result value get closer to the GT value.
Herein, the performance of the learned detector may be somewhat proportional to size(s) of database (s) for training.
In the conventional learning method, as shown in FIG. 3, an image database to be used for learning process stores a plurality of GTs in which all classes to be detected are annotated.
However, according to this conventional learning method, if a new class such as “traffic light” and “traffic sign” needs to be additionally learned on condition that the existing classes have been learned, all objects corresponding to the new class should be searched and annotated for all existing training images in the existing database. Further, newly-added training images other than the existing training images should be annotated for all the existing classes as well as the new class, resulting in an inefficiency of the learning